Many boats and other watercraft are driven by one or more outboard engines. Marine outboard engines have an engine, such as an internal combustion engine, that drives a vertically oriented driveshaft. The driveshaft is coupled to a driving gear that drives a driven gear mounted on a horizontally oriented propeller shaft that, in turn, drives a propeller to propel the boat forward.
In some applications, such as boat racing, it is desired to use a high-powered engine to provide a large amount of horsepower and torque for driving the propeller. In high-powered applications, all of the intermediate components between the engine and the propeller, such as the driveshaft, propeller shaft and the driving and driven gears therebetween, must be made correspondingly larger to reliably transmit the power, resulting in increased size and weight. In particular, the greater power requires a larger driven gear on the propeller shaft, which in turn may require a larger gear case housing. A larger gear case housing creates additional drag when the gear case housing is submerged in the body of water while the engine is being used, with an attendant decrease in performance and efficiency. In addition, because higher-powered engines require larger gear case housings than lower-powered engines, an increased number of parts must be designed, manufactured and kept in inventory and an attendant increase in manufacturing cost.
One alternative method of delivering a large amount of power to the propeller shaft is to provide two smaller driveshafts driving a single driven gear on the propeller shaft. In this arrangement, each driveshaft theoretically delivers half of the power output from the engine, and as a result each driveshaft can be smaller in size, and the driving and driven gears can be made correspondingly smaller, resulting in a lighter and more compact arrangement.
However, the arrangement having two driveshafts has drawbacks. The gears on the driveshafts and the propeller shaft generally do not mesh perfectly, due to manufacturing tolerances in the machining of the gears and difficulties in obtaining proper timing between the driving and driven gears during assembly of the engine. As a result, the power from the engine is unevenly distributed between the two driveshafts, resulting in increased and uneven wearing of the gears and the risk of applying more power to one of the driveshafts and its corresponding driving gear than they are designed to support.
One way of remedying these drawbacks is to manually attempt to mesh the teeth of the gears in numerous different arrangements, until one arrangement is found that satisfactorily balances the load between the two driveshafts. This procedure is time-consuming, resulting in increased manufacturing cost, and does not necessarily result in a complete balancing of the load.
Therefore, there is a need for a method of assembling a marine outboard engine to provide improved load balancing between the two driveshafts.
There is also a need for a marine outboard engine having improved load balancing between the two driveshafts.